1. Field of the Invention
The present invention relates to an on board refueling vapor recovery system for controlling an amount of fuel evaporative emissions released when a fuel tank of a vehicle is refilled with fuel and fuel vapor passage using for the same.
2. Description of the Related Art
Fuel evaporative emissions released from a fuel tank of a vehicle is one of the major sources of air pollution when the fuel tank is refilled with a fuel. Due to this, for example, in the United States of America, an amount of fuel evaporative emissions released at the time of refilling fuel tanks of vehicles is regulated.
To cope with an regulation of the amount of the fuel evaporative emissions, on-board evaporative recovery (called ORVR) system are equipped on vehicles so that the amount of fuel evaporative emissions is controlled. an known on board refueling vapor recovery of this type is described in the specification of Japanese Patent No. 3158170 by the applicant of this patent application (refer to FIG. 7).
In the on board refueling vapor recovery shown in FIG. 7, a fuel tank T comprises a tank main body 101 and a fuel filler pipe 102 provided to extend upwardly in an inclined fashion from the tank main body 101, and a fuel filler inlet portion 102a having a larger diameter is provided at an upper end of the fuel filler pipe 102.
In addition, one end portion of a first fuel vapor passage 103 connects to an upper portion of the tank main body 101, and a canister C for adsorbing fuel evaporative emissions released from the fuel tank T connects to the other end of the first fuel vapor passage 103.
A float valve 106 is provided at a connecting portion to the interior of the tank main body 101 of the first fuel vapor passage 103. The float valve 106 is adapted to close when a level of fuel in the tank main body 101 of the fuel tank T reaches a predetermined level to cut off a flow of the fuel evaporative emissions to the canister side. Note that in the specification, white arrows outlined with black lines in the accompanying drawings denoted directions of the fuel evaporative emissions.
Interposed at an intermediate position along the first fuel vapor passage 103 is a valve V adapted to open at the time of refueling the vehicle. A diaphragm 109 and a valve element 114 connected to the diaphragm 109 to interlock therewith are provided in the valve V, and the valve element 114 deforms to open at the time of refueling by way of a relationship between a pressure of the fuel filler inlet portion 102a inputted into the diaphragm 109 via a communication path 115 and a pressure of the fuel evaporative emissions flowing from the tank main body 101 toward the canister C.
Owing to this, the fuel evaporative emissions released from the tank main body 101 flow toward the canister C at the time of refueling.
Note that reference numeral 111 denotes a spring chamber and reference numeral 112 denotes a spring.
A second fuel vapor passage 122 is provided so that the passage branches from the first fuel vapor passage 103 (103a) which connects the float valve 106 with the valve V. The second fuel vapor passage 122 connects to the fuel filler inlet portion 102a at a position which is closer to the tank main body 102 than to a shutter 117 to constitute a circulation path for the fuel evaporative emissions.
In addition, provided at an intermediate position along the second fuel vapor passage 122 is a check valve called a vapor recirculation valve 125 adapted to open to allow fuel evaporative emissions to flow from the tank main body 101 side to the fuel filler inlet portion 102a side when a differential pressure between the tank main body 101 side and the fuel filler inlet portion 102a reaches or exceeds a predetermined value.
In addition, the second fuel vapor passage 122 also serves to prevent outside air from being entrained by a flow of fuel into the tank main body 101 when the vehicle is refueled from a fuel filler nozzle.
Namely, the amount of the fuel evaporative emissions released from the tank main body 101 at the time of refueling should correspond to the amount of fuel so refilled. However, when the outside air (air) is taken into the tank main body 101 the amount of fuel evaporative emissions released from the tank main body 101 increases.
Furthermore, since the fuel evaporative emissions are promoted for reasons of saturated vapor pressure when outside air is incorporated, the amount of the fuel evaporative emissions released from the tank main body 101 increases further.
However, an incorporation of outside air is prevented or reduced by providing the second fuel vapor passage 122 for recirculation of the fuel evaporative emissions as shown in FIG. 7.
This allows the amount of fuel evaporative emissions released from the tank main body 101 can be reduced to the amount of fuel that has been refilled in the tank main body 101.
In addition, in the event that the valve V does not open due to a slow speed at which the fuel tank T is refilled with fuel, the check valve 125 prevents the release of the fuel evaporative emissions to the atmosphere from the fuel filler inlet portion 102a via the second fuel vapor passage 122. Namely, since the slow refueling speed lowers the pressure of fuel evaporative emissions attempting to flow toward the canister C, the valve V is not activated.
On the other hand, an amount of the fuel evaporative emissions corresponding to the volume of refilled fuel overflows from the tank main body 101. Here, in the event that there exists no pressure resistance in the second fuel vapor passage 122, the overflowed fuel evaporative emissions pass through the second fuel vapor passage and are eventually released to the atmosphere from the fuel filler inlet portion 102a. 
However, with the check valve 125 provided along the second fuel vapor passage 122 as shown in FIG. 7, the release of the fuel evaporative emissions to the atmosphere is restrained. Moreover, a pressure of the fuel evaporative emissions at the valve V becomes higher corresponding to an amount of the release of the fuel evaporative emissions is suppressed.
Namely, an opening of the valve V is promoted by the check valve 125 (the valve opening pressure of the check valve 125 is set to be slightly higher than that of the valve V). When the valve V opens fuel evaporative emissions flow through the first fuel vapor passage 103 (103a, 103b) toward the canister C, whereby the release of the fuel evaporative emissions to the atmosphere is restrained.
Thus, the second fuel vapor passage 122 and the check valve 125 provided therealong play an important role in on board refueling vapor recovery.
Here, the check valve 125 is shown in FIG. 8.
As shown in FIG. 8, the check valve 125 has an inlet side hose opening 125a, an outlet side hose opening 125b and a valve chamber 125c. A valve seat Vs is formed in the valve chamber 125c. A valve element Vb is inserted in the valve chamber 125c, and the valve element Vb is biased toward the valve seat Vs by means of a spring S.
An orifice is formed in the valve element Vb, and even if the check valve 125 is in a closed condition, a slight amount of fuel vapor is allowed to flow through the check valve 125.
Incidentally, in the case of the check valve 125 shown in FIG. 8, in an attempt to assemble the check valve 125 to the second fuel vapor passage 122, an inlet side hose 122a of the second fuel vapor passage 122 must connect to the inlet side hose opening 125a, while an outlet side hose 122b of the second fuel vapor passage 122 must connect to the outlet side hose opening 125b. 
In addition, in an attempt to install the check valve 125 and hence the on board refueling vapor recovery in a limited space, the check valve 125 needs to be miniaturized both in size and weight to reduce the installation space. Additionally, the amount of fuel evaporative emissions needs to reduced further.